Synthesis of imines

Selective transformations Selective styrene ring opening [103] One-pot domino process for regioselective synthesis of a-carbonyl furans [104] Tandem process for synthesis of quinoxalines [105] Atmospheric oxidation of toluene [106] Cyclohexane oxidation [107] Synthesis of imines from alcohols [108] Synthesis of 2-aminodiphenylamine [109] 9H-Fluorene oxidation [110] Dehydrogenation of ethane in the presence of C02 [111] Decomposition of methane [112] Carbon monoxide oxidation [113]... 

Kumar, R., Sithambaram, S. and Suib,S.L. (2009) Cyclohexane oxidation catalyzed by manganese oxide octahedral molecular sieves - effect of acidity of the catalyst. Journal of Catalysis, 262,304—313. Sithambaram, S., Kumar, R., Son, Y. and Suib, S.L. (2008) Tandem catalysis direct catalytic synthesis of imines from alcohols using manganese octahedral molecular sieves. Journal of Catalysis, 253, 269-277. 

Shibasaki et al. developed a polymer-supported bifunctional catalyst (33) in which aluminum was complexed to a chiral binaphtyl derivative containing also two Lewis basic phosphine oxide-functionahties. The binaphtyl unit was attached via a non-coordinating alkenyl Hnker to the Janda Jel-polymer, a polystyrene resin containing flexible tetrahydrofuran-derived cross-Hnkers and showing better swelling properties than Merifield resins (Scheme 4.19) [105]. Catalyst (33) was employed in the enantioselective Strecker-type synthesis of imines with TMSCN. 

Varma, R.S. and Dahiya, R., Microwave-assisted facile synthesis of imines and enamines using envirocat EPZG as a catalyst, Synlett, 1997, 1245. 

Pyridine-2,6-dicarbaldehyde and 2,6-diacetylpyridine have been widely used in the template synthesis of imine chelates ranging in complexity from linear tridentates, such as (17),38 39 to macrocyclic structures with a range of ring sizes, such as (18).40-42 The in situ formation of macrocyclic ligands of this type depends upon the ring size and the strength of complexation of the triamine by the metal ion at the pH of the reaction. Related complexes with an additional donor atom attached to R2 have been synthesized also.43 44... 

The importance of the metal-metal contacts in these reactions is confirmed when ethylenediamine is treated with the same ketones in the absence of one of the metals, a process from which the starting materials are recovered unaltered neither imine nor diimine can be prepared under these conditions. In this sense, it is interesting to note that the methods previously reported for the synthesis of imines always require high temperatures, prolonged reaction periods, and the presence of dehydrating agents. In contrast, the reaction between [AuTlR2(en)] and the ketones takes place even in the gas phase and in a few seconds. 

In the synthesis of imines and enamines by this method, the water produced in the reaction must be removed azeotropically to drive the reaction to the right. In aqueous acid, equilibrium conditions favor the ketone rather than the imine. This relationship is the reason why Grignard reaction of a nitrile provides a good route to the synthesis of ketones. The intermediate imine formed is hydrolyzed easily to the corresponding ketone (e.g., the transformation of 3-3 to 3-4 in Example 3.13). 

Pyridine-2,6-dicarbaldehyde and 2,6-diacetylpyridine have been widely used in the template synthesis of imine chelates ranging in complexity from linear tridentates, such as to... 

Methods for the preparation of hydrazones and oximes differ little from those used for the synthesis of imines from ketones and aldehydes in that the appropriate nitrogen species and the ketone are mixed. However, the equilibrium for the majority of reactions of ketones and aldehydes with hydrazines and hy-droxylamine favor the product hydr nes and oximes and removal of the water formed by the condensation is not required. 8(> Acid catalysis is complicated by the basicity of the reagent and, for example, the maximum rate of oxime formation is at approximately pH 4. Complicating reactions can occur such as the 1 2 combination of hydrazine with two ketones or aldehydes to form azines but this is not a problem with the substituted hydrazines that are used for asymmetric induction. 

Under strictly anhydrous conditions, the iminophosphorane intermediate that is formed as a result of the Staudinger reaction can react with aldehydes and ketones in an intermolecular fashion (as in the synthesis of imine 36 described above) or intramolecularly with a variety of carbonyl containing functional groups to afford a host of products. Nitrogen containing ring systems such as cyclic imines (44) represent just one of the many products one can prepare and the reaction is particularly well suited for the facile synthesis of five, six, and seven-membered rings. In addition to aldehydes and ketones, carboxylic acids, esters, thio-esters, and amides can also react in an intramolecular fashion to trap an iminophosphorane to afford a variety of heterocycles. Examples from the current literature are described in Section 2.5.5. 

Among monoamines, both enantiomers of 1-phenylethylamine and their derivatives play a prominent role. They are commercially available, but can also be prepared by resolution of the racemate, obtainable by Leuckart- Wallach reaction of acetophenone1, with malic acid2 or, more conveniently, with tartaric acid in methanol3. They are used as chiral additives for the addition of zinc alkyls to aldehydes in Section D. 1.3.1.4., as copper complexes for the synthesis of biaryls in Section B.2., as lithium salts for enantioselective deprotonation in Section C., and as imines in Sections D.1.1.1.3.1., D.1.1.1,4.. D.1.4.4., D.1.5.2., D.1.5.8., D. 1.6.1.2.1., D.2.3.I., and D.8. A general procedure for the synthesis of imines from carbonyl compounds and primary amines, with many examples of both chiral carbonyl compounds and chiral amines is given in reference 4. 

Microwave-expedited condensation reactions using montmorillonite KIO clay or Envirocat reagent, EPZG , have yielded a rapid synthesis of imines and enamines via the reactions of primary and secondary amines with aldehydes and ketones, respectively (Scheme 2.2-32) [97,98]. In these reactions, the generation of polar transition-state intermediates that readily couple to microwaves is probably responsible for the rapid imine or enamine formation. The use of a MW oven at lower power levels or intermittent heating has been used to prevent the loss of low-boi-Hng reactants. 

Scheme 3.10) [3], Equimolar amounts of either benzidine or p-toluidine were used (in synthesis of imine 46 and fc -imine 47, respectively) and after reaction completed, products did not need any purification. On the other hand, solution reaction required reflux for longer time, with lower yield in the case of benzidine (5h, 60% yield). Manual grinding in mortar afforded after 30min products in considerably lower yields. 

Yadav DKT, Bhanage B (2014) Base-mediated synthesis of imines and amines from Al-phenylureas and alcohols. Synlett 25 1611-1615... 

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